This invention relates to a generally flat glazed article that is produced by firing in a kiln, such as a glazed dinner plate.
A glazed dinner plate is fired while standing on a saggar. Because the glaze will stick fast to the saggar during the firing process, it is important that any part of the plate that will be in contact with the saggar should be free from glaze.
A typical plate has a foot-ring on which it stands. This foot-ring is a small protrusion from the underside of the generally flat plate. Normally, it has the same general form as the outline of the plate, being for instance circular on a circular plate and, for ease of manufacture, a continuous circle. However, it is also possible to have a foot-ring which comprises only segments of the circle or the other appropriate geometric shape, which is normally similar to the shape of the outline of the plate. In any case, the bottom of this foot-ring is the only part of the plate to come in contact with the saggar during firing. Consequently, all parts of the plate other than the bottom of the foot-ring may be covered with glaze.
According to the conventional manufacturing technique, the plate is first totally covered with glaze and the bottom of the foot-ring is wiped clean prior to firing. As a result the bottom of the foot-ring remains unglazed, leaving the finished plate with a rough surface which, even after polishing, remains slightly abrasive. When plates are stacked, one upon another, the unglazed bottom of the foot-ring of one plate stands upon the glazed upper surface of the plate beneath, and can scratch the glaze. When large numbers of plates are staked on a regular basis, such as in an hotel or other catering establishment, the risk of scratching is increased. The very action of stacking or unstacking plates means that the unglazed bottom of the foot-ring is drawn across the glazed upper surface of the plate beneath. In a tall stack the weight of the plates above presses each plate hard against the one beneath. The daily movement of such stacks of plates from wash place, to storage area, to dining area, and back again, tends further to increase this scratching effect by grinding the plates one upon another, so that the glaze on the upper surface of the plates becomes dull and possibly discolored.
Various techniques have been tried to obviate or reduce this scratching effect. One solution is to glaze the bottom of the plate's foot-ring so that it will be as smooth as the rest of the plate. This is achieved by glazing the whole plate, and then firing it while it is supported from below on three pins. However, this requires that the plate be sufficiently rigid to stand on the pins without distortion. This necessary rigidity can only be achieved by pre-firing the plate, which makes the manufacturing process more complicated and expensive. In addition, the three pins leave small defects in the glaze of the underside of the plate. Moreover, because such plates are uniformly shiny, they tend to slide about when stacks of plates are moved, increasing the risk of breakages.
Another method of avoiding the problem is to shape the plate so that, when it is stacked on a similar plate, only the rim of the plate is in contact with the next plate. Such a technique requires that the rim of the plate has an edge portion with an enlarged vertical extension to enable one plate to "hang" in another without its foot-ring touching the upper surface of the plate below. This gives the plate a "bowl" profile, which may not be acceptable for normal dinner plates. Such plates are also more difficult to handle when stacking and unstacking them in large numbers.